HIV-1, the predominant cause of AIDS in humans, is unable to replicate in most non-human species. Therefore, the most practical animal model of human AIDS consists of infection of rhesus macaques with SIVMAC or chimeras derived from SIVMAC. However, the usefulness of these models is limited by the fact that HIV-1 and SIVMAC are distinct viruses. Based on an understanding of species-specific restriction factors, we have generated recombinant viruses, named simian tropic HIV (stHIV), that are almost entirely derived from HIV-1 but can replicate in pigtailed macaques. During the last funding cycle we have used animal adaptation to develop stHIV isolates that cause AIDS in pigtail macaques. Additionally, we have studied the effects of known restriction factors on stHIV replication and unveiled the activity of novel, as yet unidentified, inhibitors that are induced by IFN? and limit lentiviral replication in a species-specific manner in primary cells. The aims of this proposal are to further develop stHIV by generating infectious molecular clones that are consistently pathogenic following mucosal challenges in both pigtail and rhesus macaques and are based on HIV-1 strains circulating in humans. To achieve these aims our studies will include a more detailed characterization of restriction factor polymorphism and activity in macaques and how these drive virus evolution in animals. Additionally, we will identify novel IFN!-induced inhibitors that limit stHIV replication in macaque cells and generate stHIV variants that can overcome them. Our preliminary data suggest that these goals are feasible and will lead to the successful development of stHIV, an advance that has the potential to transform non- human primate models for HIV-1 drug and vaccine development.